1. Field of the Invention
The present invention concerns a method for examining a human or animal body with regard to a blood flow in the pulmonary artery. In addition the invention concerns a medical imaging apparatus for implementing such a method. Such a method is especially used in the examination of patients with a pulmonary hypertension or with a suspected pulmonary hypertension or with a pulmonary hypertension occurring when the body is under stress.
2. Description of the Prior Art
Pulmonary hypertension (abbreviated “PH” below) is an illness characterized by an increase in the pulmonary artery pressure. Pulmonary arterial hypertension (abbreviated “PAH” below) is a subgroup of PH. The definition of PAH has been established in the usual guidelines. It relates to the mean pulmonary artery pressure (mPAP) and not to the systolic pulmonary artery pressure (sPAP) and to the exclusion of basic conditions such as serious lung or left heart diseases. PAH exists if the mean pulmonary artery pressure (mPAP) exceeds 25 mm Hg at rest or 30 mm Hg under stress. By comparison, the normal pulmonary pressure at rest is below 21 mm Hg. The prognosis of the PH is bad regardless of its genesis, especially if the diagnosis is made late.
Overview articles and guidelines about pulmonary hypertension can be found in the publications Galie N et al., “Guidelines on diagnosis and treatment of pulmonary arterial hypertension”, The Task Force on Diagnosis and Treatment of Pulmonary Arterial Hypertension of the European Society of Cardiology, Eur Heart J 2004; 25(24): 2243-2278 and Olschewski H et al., “Diagnosis and therapy of chronic pulmonary hypertension” Pneumologie 2006; 60(12): 749-771.
A right heart catheter examination (swan-neck catheter) is currently seen as the “gold standard” method of examination for the determination of pulmonary artery pressure and thereby for the diagnosis of pulmonary hypertension. This examination is invasive however and must be carried out by experienced personnel to obtain reliable data and to keep the risks low. The costs of such an examination are high.
The publications Chemia D et al. “Haemodynamic evaluation of pulmonary hypertension” Eur Respir J 2002; 20: 1314-1331, Denton C P et al. “Comparison of Doppler Echocardiography and Right Heart Catheterization to Assess Pulmonary Hypertension in Systemic Sclerosis” Br J Rheumatology 1997; 36: 239-243, Laaban J P et al. “Estimation of Systolic Pulmonary Artery Pressure Using Doppler Echocardiography in Patients with Chronic Obstructive Pulmonary Disease” Chest 1989; 96: 1258-1262, and Hinderliter A L et al. “Effects of Long-term Infusion of Prostacyclin (Epoprostenol) on Echocardiographic Measures of Right Ventricular Structure and Function in Primary Pulmonary Hypertension” Circulation 1997; 95: 1479-7486 deal with methods such as the color doppler echocardiography method with which the systolic pulmonary artery pressure (abbreviated below “sPAP”) can be determined from the maximum regurgitation velocity of a tricuspid insufficiency. This method is currently used as a screening examination for establishing pulmonary arterial hypertension. For patients with PAH the sensitivity is around circa 90% and the specificity is around 67% to 75%. The accuracy of the estimation in a healthy control population is however not known. In addition the practice of computing the mPAP from the sPAP is not established.
Other alternative non-invasive methods are subordinate to color doppler echocardiography.
A method is known from the publication Kitakabe A I et al. “Noninvasive evaluation of pulmonary hypertension by a pulsed Doppler technique” Circulation 1983; 68: 302-309 in which the acceleration time of the blood stream is determined with the aid of color doppler echocardiography and used as the correlate to the logarithm of the mPAP.
A method is known from the publication Mousseaux E et al. “Pulmonary arterial resistance; noninvasive measurement with indexes of pulmonary flow estimated at velocity-encoded MR imaging—preliminary experience” Radiology 1999; 21 2(3): 896-902 in which inter alia the maximum changes over time of the blood flow is determined from one-dimensional magnetic resonance phase-contrast flow measurements in the pulmonary artery as the correlate to pulmonary vascular resistance.
Known from the publications Laffon E et al. “Noninvasive assessment of pulmonary arterial hypertension by MR phasemapping method” J Appl Physiol 2001; 90: 2197-2202, and Laffon E et al. “A computed method for noninvasive MRI assessment of pulmonary arterial hypertension” J Appl Physiol 2004; 96; 463-468 are methods in which the pressure wave velocity and the maximum blood stream velocity can be measured with the aid of one-dimensional magnetic-resonance phase-contrast flow quantities in the pulmonary artery and an optimum functional relationship to mPAP determined. These types of results were not able however to be reliably reproduced by other working groups.
In the publication Kondo C et al. “Pulmonary Flow Quantification and Flow Profile Analysis with Velocity-encoded Cine MR Imaging” Radiology 1992; 183: 751-758 the relationship is demonstrated that patients with a PH exhibit a greater proportion of retrograde blood flow in the pulmonary artery.
The publication Mohiaddin R H et al. “Visualization of flow by vector analysis of multidirectional cine MR velocity mapping”, Journal of computer assisted tomography 1994, 18: 383-392 describes how, in patients with pulmonary hypertension in the diastole, a backwards-directed flow in the pulmonary artery is detectable.
All the publications cited represent small explorative series. Most of the methods described therein have not been able to establish themselves.